OXNARD, Calif. — Taco Charlton dug his cleats into the grass and put his right hand down to complete his menacing three-point stance. Shoulder pads on and helmet strapped tight, Charlton had his first chance to showcase his skills in full pads as a member of the Dallas Cowboys during the first days of training camp.

The 6-foot-6-inch, 273-pound defensive end lined up across from offensive tackle La’El Collins. Collins was celebrating his 24th birthday with a two-year, $15.4 million contract he signed with Dallas the day before. After facing Charlton in pass-rushing drills, he had one more reason to celebrate.

Both players fired off the line on the coaches’ command. Charlton tried to get around his opposition with a spin move, but Collins didn’t bite. He stayed in front of Charlton and practically pulled a chair out from under him as the rookie defensive end plummeted to the turf.

Collins’ natural reaction was to put Charlton on his backside. He’s already proving to the Cowboys that the contract extension was worth it. As for Charlton, he’s trying to prove the first-round pick the Cowboys spent on him in this year’s draft was worth it, too. He’s off to a wobbly start.

To Charlton’s credit, he’s battling an offensive line that many deem to be the best in the league. He called Collins “one of the better tackles out there.” But Charlton didn’t solely credit Collins for his tumble in the one-on-one….